The invention relates to die stamping method and to a device for performing the method. DE 90 04 865 U1 e.g. discloses a hot stamping machine, in which to a stamping station is supplied a foil web, which has a transfer area comprising at least one layer to be transferred by die stamping.
It is admittedly known in connection with such hot stamping machines to orient the foil web with respect to its position, particularly the position of a motif periodically repeated on the transfer area, with respect to the stamping point in the stamping station in such a way that the motif is transferred in positionally precise manner to the stamping material.
However, when using such continuous foil webs it is possible for defects to occur in the foil web or in the transfer area. If such foil web or transfer area portions enter the stamping area, waste is produced, which must then be subsequently eliminated.
Problem and Solution
The problem of the invention is to reduce the production of waste in die stamping.
This problem is solved by the die stamping method and device according to the invention.
In die stamping in a stamping station a segment of a transfer area comprising at least one layer is stamped on a support or carrier material. The transfer area is supplied on a continuous foil web to the stamping station. On supplying the foil web to the stamping station it is established by a sensor means whether there are defects in the foil area of the foil web. If a defect is detected, the supply of the foil web to the stamping station is controlled in such a way that the defect is conveyed through the stamping station between two stamping operations. Therefore the defect does not pass into the printing area of the stamping station, so that no waste is produced. The procedure also has the advantage of the processing speed in the stamping station only being insignificantly influenced and the die stamping process can still be performed at high speed. This procedure is particularly advantageous if, as a result of manufacture, the foil material has defects at regular intervals. This is e.g. more particularly the case in transfer areas having holograms. The holograms can comprise individual images which are periodically repeated and diffraction gratings, optionally with patterns made therein, which are infinitely repeated on the foil. Such foils are frequently transferred to cartons and other papers, particularly packaging. This on the one hand takes place to prevent easy copying of the packaging and on the other frequently as a result of the optical and tactile effects which can be obtained.
However, foil webs stored on drums and which are used for the continuously supply of the foil web to the stamping station have attachment points, where a following foil web portion is attached to the foil web. Due to manufacture, these attachment points cannot be avoided.
According to an advantageous development of the invention the sensor means detects the electrical conductivity of the foil web.
According to further, advantageous developments of the invention, alternatively or additionally thereto, the sensor means can detect one or more optical characteristics of the foil web and it is in particular advantageous to determine the reflection behaviour thereof. According to another advantageous development the reflection behaviour is defined by a foil web-side diffraction grating. According to an advantageous development, for this purpose the sensor means has a laser light source, which directs light onto the foil web, the light intensity being detected in a diffraction maximum. It is concluded that there is a defect in the foil web, i.e. a disturbance of the diffraction grating, if the light intensity differs by a predetermined amount from the light intensity expected in this maximum.
According to a further advantageous development the sensor means comprises several sensors juxtaposed at right angles to the foil web conveying direction and it can be concluded that there is a defect in the foil web only if at least two sensors detect a signal corresponding to the existence of a defect in the foil web.
A die stamping device according to the invention is formed from a supply device for supplying foil web with the stamping foil to a stamping station of a control device for influencing the supply of the foil web to the stamping station and sensors for monitoring the foil web on the stamping station supply side. The foil web is supplied to the stamping station as a function of signals of the sensor means.
The stamping station is in particular a rotary stamping station formed from a stamping roller with a stamping die and a counter-roller. Only if the die is in engagement with the foil web is a segment of the transfer area transferred from the foil web to the carrier material. The carrier material can either be supplied sheetwise or as a continuous material web.
These and other features can be gathered from the claims, description and drawings and the individual features, either singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is hereby claimed. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder.